mRNA spindle localization and mitotic translational regulation by CPEB1 and CPEB4

Abstract

Transition through cell cycle phases requires temporal and spatial regulation of gene expression to ensure accurate chromosome duplication and segregation. This regulation involves dynamic reprogramming of gene expression at multiple transcriptional and posttranscriptional levels. In transcriptionally silent oocytes, the CPEB-family of RNA-binding proteins coordinates temporal and spatial translation regulation of stored maternal mRNAs to drive meiotic progression. CPEB1 mediates mRNA localization to the meiotic spindle, which is required to ensure proper chromosome segregation. Temporal translational regulation also takes place in mitosis, where a large repertoire of transcripts is activated or repressed in specific cell cycle phases. However, whether control of localized translation at the spindle is required for mitosis is unclear, as mitotic and acentriolar-meiotic spindles are functionally and structurally different. Furthermore, the large differences in scale-ratio between cell volume and spindle size in oocytes compared to somatic mitotic cells may generate distinct requirements for gene expression compartmentalization in meiosis and mitosis. Here we show that mitotic spindles contain CPE-localized mRNAs and translating ribosomes. Moreover, CPEB1 and CPEB4 localize in the spindles and they may function sequentially in promoting mitotic stage transitions and correct chromosome segregation. Thus, CPEB1 and CPEB4 bind to specific spindle-associated transcripts controlling the expression and/or localization of their encoded factors that, respectively, drive metaphase and anaphase/cytokinesis.

Orb-dependent polyadenylation contributes to PLP expression and centrosome scaffold assembly

“…Analysis of the gene ontologies (GO) within the common genes using the cellular component function in PANTHER uncovered significantly enriched ontologies related to the centrosome, as represented by PCNT/plp, CEP192/Spd-2, and PLK1/Polo mRNAs ( Figure S2A, Table S2 ) (Mi et al, 2021). In accordance, recent work shows CPEB1 is required for the translation and recruitment of PLK1 to centrosomes (Pascual et al, 2021). Here, we focused our subsequent analysis on PLP.…”

“…Transcriptomics uncovered thousands of direct mRNA targets of Orb and Orb2 in Drosophila S2 cells (Stepien et al, 2016). A similar analysis in HeLa cells also uncovered thousands of mRNA targets of orthologous CPEB1 and CPEB4 (Pascual et al, 2021). We compared the RNA substrates of homologous Orb and CPEB1 proteins identified in the Stepien and Pascual datasets and found 195 common genes (Hake and Richter, 1994)( Figure 2A; Table S2 ).…”

“…(A) Venn diagram shows the common mRNA targets of CPEB1 and Orb (Stepien et al, 2016; Pascual et al, 2021). Supplemental Table 2 lists overlapping mRNA targets.…”

“…Recent transcriptomics identified numerous mRNA targets of Orb from Drosophila S2 cells and CPEB1 in cultured mammalian cells (Stepien et al, 2016; Pascual et al, 2021). Among the Orb/CPEB1 mRNA targets are several mRNAs encoding centrosome proteins.…”

“…Among the Orb/CPEB1 mRNA targets are several mRNAs encoding centrosome proteins. In Xenopus and cultured mammalian cells, CPEB proteins also localize to centrosomes, and mRNAs localizing to spindle poles show enrichment of CPE motifs in their 3’-UTRs (Groisman et al, 2000; Blower et al, 2007; Eliscovich et al, 2008; Sharp et al, 2011; Pascual et al, 2021). These data are consistent with a model whereby CPEB proteins regulate components of the mitotic machinery.…”